1. Field of the Invention
The present invention relates to a method of correcting a weight unbalance of a rim-fitted tire by using a wheel balancer.
2. Description of the Related Art
It is well-known that vibrations occur if a rim-fitted tire with unbalanced weight is rotated. Such a weight unbalance includes a static unbalance in which the weight is determined without rotating the rim-fitted tire and a dynamic unbalance which occurs only when the tire is rotated.
As a method of correcting such an unbalance, nowadays, a method is mainly adopted in which the rim-fitted tire is mounted on a wheel balancer and rotated to measure the amount of unbalance requiring correction, and one balance weight is fixed at one location on each axially opposite end face of the rim, usually on each of observe and reverse rim flanges, on the basis of that measurement. In this way, the static unbalance and the dynamic unbalance are corrected simultaneously.
That is, this correcting method is called a two-plane balancing method, in which by assuming that there is one unbalance on each opposite end face of the rim, correction is effecting by fixing a correcting balance weight whose weight is equivalent to that of the unbalance is fixed to a position 180.degree. opposite to the position where the unbalance is located on each end face.
It is well-known that the static unbalance and the dynamic unbalance, whichever is present, can constitute a source of vibration for a vehicle, and that the respective unbalances exert different influences on the vehicle. That is, the static unbalance causes vertical vibration of a vehicle, while the dynamic unbalance causes abnormal vibration of the steering wheel, shimmy, and the like.
There are cases where the vertical vibration of the vehicle, the abnormal vibration of the steering wheel, and the like are caused by the uniformity of the tire (radial force variations and lateral force variations), in addition to the weight unbalance. However, an actual examination of the vibrations after complete correction of the unbalance reveals that components which are conceivably ascribable to a weight unbalance other than that based on uniformity are included. This tendency is strong when the amount of unbalance requiring correction, particularly the dynamic unbalance component, is large.
Japanese Patent Application No. 114123/1991 (U.S. Pat. No. 5,171,067) discloses am method of correcting weight unbalance of a rim-fitted tire which minimizes vertical and horizontal vibrations constituting sources of vibration of the tire in a situation where the tire is actually used. In this method, the unbalance and the dynamic unbalance are corrected separately on the basis of the magnitude of the amount of correction of unbalance and the position on the circumference of each of the rim end faces, by means of an unbalance measuring machine for simultaneously measuring an amount of correction of static unbalance and an amount of correction of dynamic unbalance. At this time, the position of the amount of correction of static unbalance on the rim periphery is calculated in such a manner as to minimize a magnitude of an amount of correction of residual dynamic unbalance. A balance weight of a magnitude corresponding to the calculated magnitude of the amount of correction of static unbalance is fixed at the calculated position on the rim periphery, and a balance weight of a magnitude corresponding to the calculated magnitude of the amount of correction of residual dynamic unbalance is fixed at the calculated position on the circumference of each of the rim end faces, thereby correcting weight unbalance.
However, the above-described conventional method of correcting weight unbalance of a rim-fitted tire has a drawback in that, when a balance weight of a magnitude corresponding to the magnitude of the amount of correction of static unbalance is fixed on the rim periphery, it is necessary to effect positioning with a high degree of accuracy not only in the circumferential direction but also in the axial direction, thereby rendering the position very difficult.